The present invention relates to a hydraulic apparatus for a continuously variable transmission for motor vehicles, and more particularly to a hydraulic apparatus which constantly varies speed ratios.
A continuously variable transmission, having a V-belt extending between driving and driven pulleys, permits control of the number of the revolutions of the driven pulley by varying the size of the V-shaped opening in either the driving pulley, the driven pulley or simultaneously varying both of the pulleys. The size of the V-shaped opening is varied by changing the amount of pressure being fed into a hydraulic cylinder of either of the pulleys. Hence, the effective diameter of the pulley can be varied by changing the amount of pressure being fed into the hydraulic cylinder, thereby allowing for a continuously varying ratio of driving pulley diameter to driven pulley diameter. The V-shaped openings on the driving and driven pulleys are each defined by an area between a fixed pulley and a movable pulley, which is dependent upon the pressure inputted to the hydraulic cylinders. In order to provide hydraulic pressure to each of the movable pulleys, a hydraulic apparatus is provided.
A prior hydraulic apparatus for a continously variable transmission was mechanically controlled as shown, for example U.S. Pat. No. 4,094,203. Hence, severe limitations were realized in the amount of potential change in the width of the pulleys and the rate at which the width changed when compared to an electronic control of the CVT.